[EMAIL PROTECTED] wrote: > I have a list of numbers and I want to build another list with every > second element multiplied by -1. > > input = [1,2,3,4,5,6] > wanted = [1,-2,3,-4,5,-6] > > I can implement it like this: > > input = range(3,12) > wanted = [] > for (i,v) in enumerate(input): > if i%2 == 0: > wanted.append(v) > else: > wanted.append(-v) > > But is there any other better way to do this.
Use slices: input[1::2] = [-item for item in input[1::2]] If you don't want to do it in-place, just make a copy: wanted = input[:] wanted[1::2] = [-item for item in wanted[1::2]] -- Leo -- http://mail.python.org/mailman/listinfo/python-list
